Onboard Carbon Capture for Ships

Onboard carbon capture and storage (OCCS) is the post-combustion removal of CO2 from a ship’s exhaust stream, followed by liquefaction and storage in pressurized cryogenic tanks aboard the vessel, with subsequent offloading to a shore-side CO2 receiving terminal. The dominant capture chemistry is amine absorption using monoethanolamine (MEA) or a proprietary hindered amine solvent. It is one of the few decarbonisation routes that can be applied to existing vessels running on conventional fuel without changing the engine or the bunker grade.

The key uncertainty over OCCS is regulatory, not technical. The technology works at pilot scale. The open question, as of mid-2025, is whether the IMO and EU frameworks will credit the captured CO2 against compliance indicators. Under the current CII framework, they do not. That single fact shapes the entire commercial case.

Why shipowners are looking at OCCS

The world fleet emits approximately 1,050 million t CO2 per year according to the IMO Fourth GHG Study (2020), about 2.9 percent of global anthropogenic emissions. Three broad paths exist to cut that number:

1. Switch to lower-carbon fuels: LNG, methanol, ammonia, biofuels, or renewable fuels of non-biological origin.
2. Cut energy demand: slow steaming, trim optimisation, weather routing, air lubrication, wind-assisted propulsion.
3. Capture and store the CO2 from continued fossil-fuel combustion at the point of emission, which is the OCCS path.

Paths 1 and 2 require either fuel availability that does not yet exist at scale or operational measures that face diminishing returns on already-optimised vessels. OCCS is attractive precisely because it decouples the decarbonisation question from the fuel question. A Capesize bulker burning heavy fuel oil for the next twelve years can, in principle, capture 60 percent of its exhaust CO2 without re-engining, without switching bunker grade, and without depending on a green fuel supply chain.

The IMO Net-Zero Framework GHG Fuel Intensity (GFI) standard from 2027 and FuelEU Maritime from 2025 together create rising compliance costs that tighten annually through 2040. OCCS becomes economically relevant to the extent that regulators credit the captured CO2, and that CO2 receiving infrastructure is available in the ports the vessel calls.

The amine absorption process

The dominant OCCS chemistry in marine pilots is chemical absorption using an amine solvent. The exhaust gas, after passing through any exhaust gas cleaning system (scrubber), is cooled from its stack temperature of approximately 250 to 350 degrees C to the absorber inlet temperature, typically 40 to 60 degrees C, using a direct-contact cooler or finned heat exchanger.

The cooled exhaust enters an absorber column where it contacts the lean amine solvent flowing downward. CO2 reacts with the amine to form a carbamate compound, loading the solvent. The CO2-rich solvent leaves the bottom of the absorber and is pumped to a stripper column, where it is heated to 110 to 130 degrees C using steam. The heat drives off the CO2 as a concentrated stream, regenerating the lean solvent which returns to the absorber. The CO2 stream is dehydrated, compressed, and liquefied for tank storage.

The principal energy cost of this cycle is the steam for solvent regeneration. For generic 30 percent MEA, regeneration heat is approximately 3.0 to 4.5 GJ per tonne of CO2 captured. Proprietary hindered amines substantially reduce this:

• KM CDR Process / KS-21 (Mitsubishi): approximately 2.5 GJ/t CO2. Used in the MOL CC-Ocean demonstration on the coal carrier Corona Utility from 2021.
• Just Catch (Aker Carbon Capture): proprietary mixed amine, approximately 2.8 to 3.2 GJ/t CO2. Used in the Wartsila and Aker marine pilot collaboration.
• Cansolv DC-103 (SLB): the dominant land-based solvent, approximately 3.0 GJ/t CO2, adapted for marine.

Solvent loss through oxidative degradation, thermal degradation, and vapour carryover is approximately 0.3 to 1.5 kg MEA-equivalent per tonne of CO2 captured, requiring periodic topping-up and generating degradation products (including trace nitrosamines) that must be treated as hazardous waste.

Capture rate and energy penalty

Capture rate (the fraction of exhaust CO2 removed) and energy penalty (the parasitic load as a percentage of total fuel input) are the two performance parameters that determine whether OCCS makes economic sense on a specific vessel.

For an amine absorption system at 70 percent capture rate, the energy balance breaks down approximately as follows:

where $E_{\text{regen}}$ (steam for stripper regeneration) contributes roughly 60 to 75 percent of the total, $E_{\text{compress}}$ (CO2 compression and liquefaction) roughly 15 to 25 percent, and $E_{\text{pumps}}$ (solvent circulation, exhaust fans, refrigeration) roughly 5 to 15 percent.

In specific numbers, for a 70 percent capture rate with a low-energy proprietary amine:

where $m_{\text{CO2, captured}}$ is the daily captured CO2 mass (t/day), $H_{\text{regen}}$ is the solvent regeneration enthalpy (approximately 2.5 to 3.5 GJ/t CO2 for proprietary amines), and $\text{LHV}_{\text{fuel}}$ is the lower heating value of the fuel (approximately 40.2 GJ/t HFO).

A worked example for a Panamax bulk carrier burning 30 t HFO/day: exhaust CO2 production is $30 \times 3.114 = 93.4$ t CO2/day. At 70 percent capture: $0.70 \times 93.4 = 65.4$ t CO2/day captured. Regeneration energy at 3.0 GJ/t: $65.4 \times 3.0 = 196$ GJ/day. Engine fuel energy input: $30 \times 40.2 = 1{,}206$ GJ/day. Energy penalty: $196 / 1{,}206 = 16.3$ percent. A large share of this can be recovered from the engine waste heat recovery system, as the exhaust contains roughly 25 to 30 percent of the engine fuel energy in recoverable form. With full waste-heat integration, the net penalty on fuel consumption drops to approximately 8 to 12 percent for a 70 percent capture rate.

The relationship between capture rate and energy penalty is approximately linear for amine systems. First-generation marine designs targeting 40 to 50 percent capture carry energy penalties of 6 to 10 percent. Second-generation designs at 60 to 70 percent carry 8 to 14 percent. Design-phase newbuild targets above 85 percent carry 14 to 20 percent.

System components

A marine OCCS installation consists of five linked subsystems.

Exhaust pre-treatment. The raw exhaust contains sulphur dioxide, NOx, particulates, and water vapour, all of which degrade or poison amine solvents. A direct-contact cooler and wash stage removes most of this before the absorber. Vessels already running a wet scrubber for MARPOL Annex VI sulphur compliance can often integrate this step into the existing scrubber water circuit.

Absorber column. A packed or structured-packing column, typically 15 to 25 m tall and 1 to 4 m in diameter depending on the exhaust flow rate and target capture rate. The principal marinisation challenge is that conventional packing loses efficiency above approximately 5 degrees of inclination; marine designs use purpose-built packing geometries or sectionalized columns with liquid redistribution to tolerate ship motion.

Stripper column and reboiler. The regeneration section, heated by steam. Waste heat from the main engine and exhaust gas economizer provides much of the steam demand; the balance comes from an auxiliary boiler or an electric heater drawing from the shaft generator.

CO2 compression and liquefaction train. The regenerated CO2 stream (approximately 95 to 99 percent purity after dehydration) is compressed to 15 to 25 bar and cooled to approximately minus 25 to minus 50 degrees C for liquefaction and storage. The cold-side energy is provided by a dedicated refrigeration compressor.

Cryogenic CO2 storage tanks. Type C pressure vessels insulated to maintain liquid CO2 at approximately minus 50 degrees C and 7 to 12 bar. The tank capacity determines how long the vessel can operate before it must offload. A Panamax bulk carrier capturing 65 t CO2/day would fill 1,000 m3 of tank volume in roughly 10 to 12 days, equivalent to a typical round voyage before a port call.

Alternative capture technologies

Amine absorption dominates current marine pilots, but three other approaches are in development.

Membranes are attractive for the low energy demand but suffer from large footprint (membrane area scales with flow rate) and limited purity. Cryogenic separation delivers liquid CO2 directly but carries a very high energy penalty. Solid sorbents avoid liquid solvent handling issues but the cycling mechanics are difficult in a marine environment. All three are at least five years behind amine absorption in readiness for commercial marine deployment.

CO2 storage and offloading

Onboard tank design

The standard choice for marine CO2 storage is semi-refrigerated liquid CO2 in Type C pressure vessels at minus 50 degrees C and 7 to 12 bar. This mirrors the technology used for small-scale LNG bunkering and LPG transport. The tanks are fabricated from austenitic stainless steel or high-nickel alloy steel to tolerate the low temperature; standard carbon steel becomes brittle below approximately minus 20 degrees C.

Tank size requirements depend on voyage length and capture rate. For a VLCC running at 60 percent capture rate for 14 days between port calls, the CO2 production is approximately:

where $\rho_{\text{CO2, liquid}} \approx 1{,}100$ kg/m$^3$ at the storage conditions. A VLCC burning 80 t/day HFO at 60 percent capture for 14 days accumulates $80 \times 3.114 \times 0.60 \times 14 / 1.10 \approx 1{,}900$ m$^3$ of liquid CO2. That is a substantial volume, roughly 2 to 3 percent of the vessel’s cargo space, and must be found either by displacing cargo tanks or by building additional structure.

CO2 offloading infrastructure

The biggest practical constraint on OCCS deployment is not the capture technology: it is the absence of CO2 receiving terminals in most ports. Offloading requires a cryogenic liquid transfer arm or flexible hose system, a shore-side buffer tank, and either direct pipeline connection to a CO2 transport network or onward shipment by CO2 tanker. As of 2025:

• Northern Lights (Oygarden, Norway): the world’s first commercial CO2 receiving terminal for ship-transported CO2, operational since 2024. Phase 1 capacity 1.5 million t/y; CO2 piped to the Aurora sub-seabed storage site in the North Sea. Operated by an Equinor, Shell, TotalEnergies joint venture.
• Porthos (Rotterdam): under construction, targeting 2.5 million t/y capacity and 2026 start. CO2 piped to depleted offshore gas fields in the North Sea.
• HyNet (Liverpool/Stanlow, UK): targeting approximately 4.5 million t/y, 2027 start. CO2 stored in depleted gas fields in Liverpool Bay.
• East Coast Cluster (Teesside, UK): targeting approximately 4 million t/y, 2028 start.

DNV’s 2024 infrastructure projection counts approximately 30 to 50 commercial CO2 receiving ports worldwide by 2030, concentrated in Europe, Japan, Korea, the US Gulf Coast, and Australia. Even under that optimistic projection, the vast majority of the world’s ports will have no CO2 receiving capability in 2030. A vessel calling only at Asian or West African ports can install a capture system but will have nowhere to offload.

CO2 utilisation routes

Geological storage is not the only exit for captured CO2. Utilisation routes (CCUS rather than CCS) include:

• Synthetic fuel production: captured CO2 plus green hydrogen to produce e-methanol or e-LNG for use as marine fuel, closing a partial carbon loop. The methanol as marine fuel economics improve substantially if the ship itself supplies the CO2 feedstock.
• Mineral carbonation: incorporation into concrete or aggregates.
• Industrial gas supply: food-grade CO2 for carbonated beverages and greenhouses.
• Enhanced oil recovery: injection into oil reservoirs (carbon-neutral only if a matching quantity is permanently stored elsewhere).

Utilisation markets are smaller and more fragmented than geological storage markets, but they may offer premium pricing for verified, high-purity marine-sourced CO2.

Regulatory crediting: the key uncertainty

The commercial case for OCCS depends entirely on whether the captured CO2 is deducted from the compliance metrics. Here the situation is complicated and differs between IMO and EU frameworks.

IMO CII and GFI: no credit yet

Under the CII framework (MARPOL Annex VI Regulation 28, as amended by MEPC.337(76) and the 2023 revised guidelines MEPC.355(78)), the attained CII is calculated from reported fuel consumption multiplied by the appropriate CO2 conversion factor. Captured CO2 is not subtracted from this calculation. A vessel that captures and stores 60 percent of its exhaust CO2 receives no CII benefit under the current text.

IMO MEPC 80 (July 2023) agreed to include OCCS in the work programme for the IMO Net-Zero Framework, and MEPC 81 (March 2024) advanced that work. The GFI standard under the net-zero framework is designed to use a well-to-wake GHG intensity metric, and there is a structural pathway to credit captured and permanently stored CO2 within that metric. However, no amendment has been adopted, and the precise verification and accounting methodology remains under development. Until an amendment is formally adopted and enters force, OCCS provides no CII or GFI compliance benefit.

This is the single most important fact for any commercial assessment: OCCS does not currently help a vessel meet its CII rating or its EEXI requirement.

EU ETS: conditional deduction

Under the EU ETS for shipping (EU ETS for shipping from 2024), Directive 2003/87/EC as amended by Directive 2023/959/EU explicitly allows a deduction for CO2 that is “captured and transported to a storage site for permanent geological storage pursuant to Directive 2009/31/EC.” The deduction is allowed only when:

1. The CO2 is permanently stored (not utilised) in an EU-recognised geological storage facility.
2. The capture, transfer, and storage chain is verified under the EU MRV Regulation (EU MRV Regulation).
3. An accredited verifier confirms the mass of captured CO2 and the integrity of the offloading and storage documentation.

Practically this means a ship calling at Northern Lights (which connects to the Aurora North Sea storage site) and meeting the MRV verification requirements can deduct the transferred CO2 from its EU ETS surrender obligation. At an EUA price of EUR 60 to EUR 80 per tonne (the approximate 2024 to 2025 range), this represents a material financial benefit.

CO2 that is offloaded but used industrially (for beverages, concrete, EOR) does not qualify for the deduction. It must be permanently stored.

FuelEU Maritime: captured CO2 can reduce GHG intensity

The FuelEU Maritime Regulation (EU 2023/1805), in force from 1 January 2025, sets a GHG intensity limit (gCO2eq per MJ of energy used) that tightens every five years from 2025. The regulation defines “renewable and low-carbon fuels” by their well-to-wake GHG intensity and explicitly provides for OCCS in its Annex I GHG intensity methodology: CO2 that is captured at the point of emission on the vessel and permanently stored does not count toward the vessel’s GHG intensity denominator.

The practical challenge is the same as for EU ETS: the storage must be permanent and certified. Captured CO2 offloaded at Northern Lights and stored in the Aurora field qualifies. Captured CO2 used for synthetic fuel production at an onshore e-methanol plant is treated differently and depends on whether the resulting fuel enters the vessel’s energy balance.

The MAC curve calculator (lifecycle MAC curve) and the three-regime cost bridge (lifecycle three-regime cost) can model the abatement economics across CII, ETS, and FuelEU simultaneously.

Classification society Approval in Principle

Classification societies have moved ahead of the IMO regulatory framework in recognising OCCS. Approval in Principle (AiP) does not constitute class approval for a specific vessel but establishes that the concept has been reviewed and found to be technically sound, enabling detailed design work to proceed.

Each AiP covers the principal subsystems: the absorber-stripper plant, CO2 compression and liquefaction, cryogenic Type C storage tanks, and the offloading interface. The class guidance notes also address the CO2 storage hazards (asphyxiation risk, cold shock, pressure relief) and the intact stability and damage stability implications of the added weight.

Pilot and demonstration projects

MOL CC-Ocean (2021 to present)

Mitsui O.S.K. Lines (MOL), Mitsubishi Shipbuilding, Mitsubishi Heavy Industries, and ClassNK installed a small-scale CO2 capture unit on the coal carrier Corona Utility in 2021. The initial pilot captured approximately 0.1 to 1 t CO2/day, roughly 5 percent of the exhaust CO2, using the Mitsubishi KS-21 hindered amine solvent. The demonstration confirmed the marinisation of the capture chemistry and the feasibility of the absorber column under ship motion. A larger-scale follow-on system targeting approximately 100 t CO2/day (40 percent capture rate) was under development for newbuild delivery in 2025.

Value Maritime Filtree (2023 to present)

Value Maritime (Netherlands) developed a containerized combined scrubber and carbon capture unit called the Filtree. The system is sold as a box: it fits into a standard 40-foot footprint, handles SOx scrubbing and CO2 capture simultaneously, and targets approximately 40 percent capture rate. By the end of 2024, approximately 6 vessels had Filtree systems installed, predominantly smaller chemical tankers and inland waterway barges. The system captures CO2 as a liquid and stores it in an integrated tank within the containerized unit, which is swapped out at port and replaced with a fresh unit.

Wartsila and Aker Carbon Capture (2022 to present)

Wartsila and Aker Carbon Capture (now part of SLB) announced a joint marine CCS development programme in 2022. Their first marine installation used the Aker Just Catch amine technology on a pilot arrangement with Stena Bulk’s chemical tanker Stena Impero, capturing approximately 4 t CO2/day at roughly 20 percent capture rate. The collaboration has since announced several additional pilot agreements for 2024 to 2026 delivery.

Solvang Clipper Eos (2023 to present)

Solvang ASA installed a Wartsila-supplied OCC system on the LPG carrier Clipper Eos, reporting approximately 70 percent capture rate, the highest demonstrated on a commercial vessel as of 2024. The result confirmed that high capture rates are achievable on a vessel in commercial operation, though the LPG carrier hull form provides more available deck space than a bulk carrier or container ship of similar engine power.

Mitsubishi Heavy Industries newbuild orders (2024 to 2027)

Mitsubishi Heavy Industries (MHI) announced approximately eight newbuild OCCS orders for delivery between 2025 and 2027, principally on coal carriers and LNG carriers operated by NYK, MOL, and K Line. Each system is designed for 60 to 85 percent capture rate. These represent the first newbuild-integrated OCCS designs, in which the capture plant space, the CO2 tank volume, and the waste-heat routing are incorporated into the ship’s basic design rather than retrofitted.

Other evaluations

A.P. Moller-Maersk and Hapag-Lloyd have undertaken concept studies on retrofitting OCCS to their methanol and LNG dual-fuel container fleets. Neither has announced firm orders as of mid-2025. Both have stated publicly that they view OCCS as a potential complement to alternative fuels for the residual fossil-fuel fraction of dual-fuel operation, not as a primary decarbonisation strategy.

TECO 2030 (Norway) has been developing a marine OCCS system in partnership with several Norwegian shipping companies and has received AiP from DNV for its cartridge-based approach using a solid sorbent, targeting smaller vessels (up to approximately 20,000 DWT) where amine absorber column height is a binding constraint.

Safety and stability implications

CO2 storage hazards

Liquid CO2 at minus 50 degrees C and 7 to 12 bar presents hazards not encountered with conventional liquid fuels. A sudden tank rupture or transfer line failure produces a dense cold gas cloud: CO2 at 1.5 times the density of air, cold enough to liquefy atmospheric moisture, carrying asphyxiation risk at concentrations above 5 percent v/v (which is reached within seconds at close range). Cold shock to carbon steel from accidental liquid CO2 contact can cause brittle fracture. Pressure relief must be routed to a safe location, typically a high vent mast well clear of accommodation spaces and air intakes.

The IMO IGF Code framework provides analogous guidance for LNG storage, and class guidance notes (notably the ABS 2022 Guide) draw on that framework. Full IMO-level rules for CO2 storage onboard ships are under development at the IMO Sub-Committee on Carriage of Cargoes and Containers (CCC).

Solvent toxicity

The onboard amine solvent inventory is typically 50 to 200 tonnes for a working system. Monoethanolamine causes skin and eye burns on contact and is harmful if inhaled. Degradation products include trace quantities of nitrosamines (potentially carcinogenic). Crew handling solvent top-up or reclaimer sludge requires full chemical protective equipment, and the spill containment design must prevent solvent reaching the bilge or the sea.

Stability and trim

The OCCS installation adds 100 to 500 t of dry weight (absorber, stripper, heat exchangers, piping, pumps) plus the CO2 tanks (200 to 1,500 t dry, up to 5,000 t liquid CO2 at full storage). This weight must be included in the intact stability and damage stability booklets. Newbuild integrated designs accommodate the weight and free surfaces in the basic design; retrofit designs require a re-stability submission to Class and may require ballast adjustment or permanent ballast to maintain adequate GM. The hydrostatics and Bonjean curves and trim and list calculations all require updating.

Capital and operating cost

Capital cost estimates for marine OCCS retrofits in 2024 to 2025:

A newbuild-integrated design reduces CapEx by approximately 20 to 30 percent relative to a retrofit on an equivalent vessel.

Operating cost per tonne of CO2 captured (excluding capital amortisation):

• Solvent top-up and disposal: approximately USD 3 to 7 per tonne CO2
• Maintenance: approximately USD 3 to 8 per tonne CO2
• Crew time: approximately USD 1 to 3 per tonne CO2
• Fuel premium for the energy penalty: approximately USD 25 to 60 per tonne CO2 (variable with fuel price)
• CO2 offloading fee at port: approximately USD 20 to 80 per tonne CO2 (highly variable; early projects have offered free offloading to seed the market)

Total operating cost: approximately USD 55 to 160 per tonne CO2. Adding capital amortisation over a 15-year asset life adds USD 30 to 80 per tonne CO2. The all-in abated cost is approximately USD 85 to 240 per tonne CO2 in 2025, with a learning-curve projection toward USD 60 to 120 per tonne by 2030.

At EU ETS prices of EUR 60 to 80 per tonne (2024 to 2025 range), the economics are marginal for the EU ETS benefit alone. With FuelEU Maritime penalty avoidance added, the combined regulatory value approaches EUR 100 to 200 per tonne by 2030, which begins to justify the all-in cost on larger vessels. The retrofit payback calculator (lifecycle retrofit payback) models this across varying EUA price assumptions.

Limitations

Regulatory crediting is not yet in place. The most important limitation is not technical. Until IMO formally amends the CII or GFI calculation methodology to credit captured and stored CO2, OCCS delivers no compliance benefit against the metrics that determine vessel ratings and charter attractiveness. The EU ETS credit exists but only for CO2 directed to certified geological storage, which is available at very few ports.

Port infrastructure remains a critical bottleneck. Even a shipowner fully convinced of the technology faces the constraint that most of the world’s ports cannot receive liquid CO2 in 2025. A vessel trading on routes that do not call at Northern Lights, Rotterdam, or a handful of other European ports has nowhere to offload. This constraint will ease as North Sea CCS infrastructure expands through 2028 to 2032, and as Japan and Australia develop receiving terminals, but it is binding today.

Space and weight on existing vessels. The absorber column height (15 to 25 m) and the CO2 tank volume requirement (potentially 1,500 to 2,500 m3 on larger vessels for a 14-day voyage) are difficult to accommodate on vessels not designed for them. Container ships and bulk carriers have limited void space not used for cargo. Retrofits require detailed space studies, structural reinforcement, and re-stability submissions. Many vessels will prove unretrofittable without major structural modification.

Energy penalty increases fuel costs. An 8 to 14 percent energy penalty on a vessel burning 80 t HFO/day means 6 to 11 extra tonnes of fuel per day. At USD 600 per tonne HFO, that is USD 3,600 to 6,600 per day in additional fuel cost, offset only to the extent that waste-heat recovery can supply the regeneration steam. This makes OCCS less attractive on vessels that are already highly optimised for fuel consumption through slow steaming and energy-saving devices retrofits.

Solvent supply chain at scale. Fleet-wide OCCS deployment at even 10 percent penetration would require approximately 100,000 to 300,000 t/y of MEA-equivalent solvent. Global MEA production capacity is approximately 1 million t/y, principally serving industrial uses. A major capacity expansion in the amine solvent supply chain would be needed alongside the vessel installation programme.

Crew competence and training. Operating a chemical process plant at sea requires a level of process chemistry competence not in current STCW certificates. The principal equipment manufacturers (MHI, Wartsila, Aker/SLB) offer dedicated training courses (typically 5 to 10 days for engineers-in-charge, 3 to 5 days for ratings), but the global supply of trained OCCS operators is negligible in 2025.

Well-to-wake accounting for the CO2 value chain. Captured CO2 must be tracked through offloading, transport, and storage to demonstrate permanent sequestration. The well-to-wake intensity accounting framework for this scope 3 chain is still under development at both IMO and EU level. Until standardized verification methodologies exist, verifiers may apply conservative assumptions that reduce the effective credited capture fraction.

Future trajectory

DNV’s Maritime Forecast to 2050 (2023 edition) projected 200 to 800 vessels with OCCS by 2030, rising to 2,000 to 8,000 by 2040 under a scenario where the IMO net-zero framework fully credits captured CO2 and CO2 receiving infrastructure builds out as planned. These numbers represent 0.5 to 2 percent of the world fleet by number in 2030.

The vessels most likely to lead adoption are large vessels on regular routes calling at European ports (where the regulatory and infrastructure picture is clearest), vessels where the capital cost per unit of CO2 abated is lowest (VLCCs and Capesize bulkers where scale economies dominate), and newbuilds where designers can integrate the capture plant from the keel up.

The combination of OCCS with alternative fuels offers a pathway to very low net GHG intensity. LNG dual-fuel at 70 percent CO2 capture achieves a well-to-wake GHG intensity roughly equivalent to ammonia propulsion on a carbon-accounting basis, at potentially lower total system cost given current ammonia bunkering infrastructure constraints. The GFI compliance calculator (GFI compliance) models the combined fuel-plus-OCCS pathways under the net-zero framework.

The critical path items through 2030 are: IMO adoption of an amendment that credits captured and stored CO2 in the CII or GFI calculation; expansion of CO2 receiving terminals to at least 20 to 30 major global ports; standardisation of CO2 offloading equipment and interfaces (analogous to the LNG bunkering interface standardisation under ISO 20519); and a reduction in amine absorption plant CapEx through the first learning-curve phase.

Of these, the regulatory crediting decision is the one that gates the others. Until a ship can show a measurable reduction in its attained CII or its GFI from captured-and-stored CO2, the capture plant is pure cost with no compliance return, and few owners will commit the deck space, the steam, and the capital. The shore-side CO2 value chain is the same chicken-and-egg problem the alternative fuels face: terminals will not build receiving and liquefaction capacity for a CO2 stream that only a handful of ships deliver, and owners will not fit capture plants that have nowhere to discharge. This is why the demonstration projects cluster around ports already developing CO2 hubs for industrial carbon capture, such as the Northern Lights nodes in the North Sea, where the maritime stream can ride on infrastructure built for land-based emitters. The likely sequence, therefore, is that OCCS scales first on specific trades served by a CO2-ready port at one end, rather than across the fleet at once, mirroring the corridor-by-corridor pattern seen in the alternative-fuel transition.

See also

Regulatory and reporting frameworks

• IMO Net-Zero Framework
• FuelEU Maritime
• EU ETS for shipping
• What is CII?
• What is EEXI?
• EEXI, EPL and ShaPoLi
• MARPOL Annex VI
• IMO GHG Strategy
• EU MRV Regulation
• SEEMP I, II, III
• Well-to-wake GHG intensity

Alternative fuels and energy-reduction measures

• LNG as marine fuel
• Methanol as marine fuel
• Ammonia as marine fuel
• Biofuels in shipping
• Slow steaming
• Trim optimisation
• Weather routing
• Air lubrication systems
• Wind-assisted propulsion
• Just-in-time arrival
• Waste heat recovery system

Ship systems and stability

• Exhaust gas cleaning system
• Marine diesel engine
• Intact stability
• Damage stability
• Hydrostatics and Bonjean curves
• Trim and list

Ship types

• Bulk carrier
• Container ship
• Chemical tanker
• LNG carrier

Calculators

• GFI compliance calculator
• CII attained calculator
• CII required calculator
• EEXI attained calculator
• EEXI required calculator
• Lifecycle retrofit payback
• Lifecycle three-regime cost bridge
• Lifecycle MAC curve
• SEEMP measures combined
• GFI attained calculator